When to grow radishes?

Crop Genebank Knowledge Base

Radish genetic resources

Contact person for Radish: Qiu Yang, CAAS, China

Compilation of best practices

Information on current practices for genebank management of radish genetic resources was first gathered from literature and then validated and updated in collaboration with the following genebanks: CGN – Wageningen, IPK – Gatersleben; AVRDC-Taiwan, USDA Plant Genetic Resources Unit – USA, NGB – NBPGR – India, SASA – UK, WARGRU Warwick – UK.

Importance and origin


Radish roots (photo: N Bas, CGN)

Radish (Raphanus sativus L.) is an anciently annual or biennial cultivated vegetable. It most likely originated in the area between the Mediterranean and the Caspian Sea (Crisp 1995). It may come from the wild radish in southwest China (Cheo et al. 1987). It is possible that radishes were domesticated in both Asia and Europe. According to Herodotus (c. 484-424 BC), radish was one of the important crops in ancient Egypt, as radish was depicted on the walls of the Pyramids about 4000 years ago. Cultivated radish and its uses were reported in China nearly 2000 years ago (Li 1989) and in Japan radishes were known some 1000 years ago (Crisp 1995).
Based on recent studies using chloroplast single sequence repeats (cpSSRs), Yamane et al. (2009) postulate three independent domestication events which include black Spanish radish and two distinct cpSSR haplotype groups. One of the haplotype groups is geographically restricted to Asia, presenting higher cpSSR diversity than cultivated radish from the Mediterranean region or wild radish types. This implies that Asian cultivated radish cannot be traced back to European cultivated forms which spread to Asia, but might have originated from a still unknown wild species that is different from the wild ancestor of European cultivated radish (Yamane et al. 2009).
Today, radishes are grown throughout the world. Different local people prefer to use various parts of the radish plants including roots, leaves, sprouts, seed pods and oil from seeds as their food according to their own custom. Radishes are low in calories and high in vitamin C, folate, and potassium. Radishes contain sulfurous compounds, such as sulforaphane, which have anti-cancer properties, and are expectorant.
The early domestication of radishes, evolutionary processes and human selection of preferred types have led to significant variations in size, color and taste of this vegetable crop. Among them, small-rooted radishes are grown in temperate regions of the world and harvested throughout the year (Crisp 1995). Larger-rooted cultivars such as Chinese radish are predominant in East and Southeast Asia (Schippers 2004).
World production of radish roots is estimated at 7 million t per year, about 2% of the total world production of vegetables (Schippers 2004). In China, Japan and Korea, as well as in Yemen, radish ranks high in importance (Schippers 2004).

Types

  • convar. oleifera (Raphanus sativus var. oleiformis Pers.), also called R. sativus Leaf Radish Group (Wiersema and León 1999), oilseed and fodder radishes, which are grown in Southeast Asia and in Europe for leaf fodder, and as green manure.

  • convar. caudatus (Raphanus sativus var. caudatus (L.) L. H. Bailey), also known as R. sativus Rat-Tailed Radish Group (Wiersema and León 1999) – the rat-tail radish (also known as mougri, radis serpent) grown for its edible immature green or purple seed pods and leaves. This type is grown in Southeast Asia.

  • convar. sativus (Raphanus sativus var. sativus), also known as R. sativus Small Radish Group (Wiersema and León 1999), where all forms are with edible roots, leaves and germinated radish sprouts, with many different varieties but generally of the small type (radish, small radish, turnip radish, petit rave).

Raphanus sativus L. var. niger J. Kern, also known as R. sativus Chinese Radish Group with the common names Chinese radish, Japanese radish, and Oriental radish are recognized by Wiersema and León (1999) as fourth cultivated group.

Radishes can be classified in different ways: small-rooted (sometimes referred to as var. radicula) and large-rooted types (including names such as var. nigra, niger, sinensis, acanthiformis or longipinnatus) based on root size; European, Chinese, Indian and Japanese based on geography; spring or summer radish and winter radish, Chinese radish (var. longipinnatus Bailey) and all-season radish (var. radiculus Pers.) based on the adaptation to growing seasons and regions (Zhu et al. 2008).

Utilization

Radish is an important root and leafy vegetable throughout the world. The small-rooted and short-season type of radish is cultivated for salads and as fresh vegetable. The large-rooted type of radish is usually cooked, canned or pickled besides being eaten raw. The leaves and sprouts are used as salad or are cooked, too. The seed pods are cooked for soups in southwest China and Southeast Asia. People press seeds of Raphanus sativus to extract oil. Wild radish seeds contain up to 48 percent oil, which is not suitable for human consumption but has promise as a source of biofuel (http://en.wikipedia.org/wiki/Radish). Farmers also grow oil radishes to improve and fertilize the soil and as fodder. In traditional medicine, radishes are used as one of nonpoisonous materials to treat coughs, cancer, whooping cough, gastric discomfort, liver disorders, constipation, dyspepsia, gallbladder disorders, arthritis, gallstones, and kidney stones (Adams 2008).

References and further reading

Adams M. 2008. Radish. . Available from: http://www.healingfoodreference.com/radish.html. Date accessed: 21 July 2009.

George RAT, Evans DR. 1981. A classification of winter radish cultivars. Euphytica, 30(2): 483-492

Kong Q, Li X, Xiang C, Wang H, Song J, Zhi H. 2011. Genetic Diversity of Radish (Raphanus sativus L.) Germplasm Resources Revealed by AFLP and RAPD Markers. Plant Molecular Biolology Reporter. DOI 10.1007/s11105-010-0228-7

Li S. 1989. The origin and resources of vegetable crops in China. International Symposium on Horticultural Germplasm, Cultivated and Wild; Beijing, China, Sept. 1988. Chinese Society for Horticultural Science, International Academic Publishers, Beijing, pp. 197-202.

Pistrick K. 1987. Untersuchungen zur Systematik der Gattung Raphanus. Kulturpflanze 35:224-321.

Radish . Available from: http://en.wikipedia.org/wiki/Radish. Date accessed: 10 October 2009.

Thormann I, Qiu Yang, Allender C, Bas N, Campbell G, Dulloo E, Ebert AW, Lohwasser U, Pandey C, Robertson LD, Spellman O. Development of best practices for ex situ conservation of radish germplasm in the context of the Crop Genebank Knowledge Base. Genetic Resources and Crop Evolution. Published online 17 October 2012. DOI 10.1007/s10722-012-9916-5. http://www.springerlink.com/content/eg71r166jq524363/

Wiersema, JH, León B. 1999. World Economic Plants – A Standard Reference. CRC Press, USA.

Yamagishi H, Terachi T. 2003. Multiple origins of cultivated radishes as evidenced by a comparison of the structural variations in mitochondrial DNA of Raphanus. Genome 46: 89–94

Yamane K, Lü N, Ohnishi O. 2009. Multiple origins and high genetic diversity of cultivated radish inferred from polymorphism in chloroplast simple sequence repeats. Breeding Science 59: 55–65

Zhu DW, Wang DB, Li XX. 2008. Chinese crops and wild relatives, vegetable crops volume (1). Beijing: Chinese Agricultural Press.

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Radish

Radish, (Raphanus sativus), annual or biennial plant in the mustard family (Brassicaceae), grown for its large succulent taproot. The common radish is likely of Asian or Mediterranean origin and is cultivated worldwide. Radish roots are low in calories and are usually eaten raw; the young leaves can be cooked like spinach. The young fruits are also edible and are often eaten raw or sautéed. The small quick-growing spring varieties have a mild, crisp, moderately firm flesh, whereas the large, slow-growing summer and winter types have pungent firm flesh. Winter varieties can be stored through the winter.

Radish (Raphanus sativus, variety radicula).Ingmar Holmasen

Radishes are usually grown as annuals and are harvested before they flower. The lobed leaves form a basal rosette that emerges from the top of the root. Flower stalks usually appear in the first season, bearing white or lilac-veined flowers with four petals; the seeds are borne in a pod called a silicle. Depending on the variety, the edible root ranges in shape from spherical to long and cylindrical or tapered, and the outside skin can be white, yellow, pink, red, purple, or black. Radishes vary in size from a few grams in the most-popular early American and European varieties up to 1 kg (2.2 pounds) in the Japanese daikon radish.

radish rootEdible radish roots (Raphanus sativus), washed and trimmed.AdstockRF

The Radish

The Radish – A Little History and Some Growing Instructions

Radishes originated in China, and in China, today, truly wild forms of the radish can still be found. The name, radish, comes from the Latin word, radix, which means “root” and specifically radish root. The genus name, Raphanus, is a Latinized form of a Greek expression raphanos which means “easily reared”. In prehistoric times, the radish spread to Middle Asia where many different forms were developed and soon after, the radish spread to the Mediterranean. Before the pyramids were constructed, ancient Egyptian writing show that radishes were being cultivated, and the ancient Greeks so valued the radish that they offered up little gold radishes to the god Apollo. The Romans also were familiar with various forms of the radish.

In the middle ages, in both Europe and the Orient, a fascination with giant radishes was created. Giant radishes were described in Germany in the 13 th century and a German botanist reported seeing radishes weighing 100 pounds in 1544. Small radishes were not recorded in Europe and Britain until after the middle of the 16 th century, but by 1586, small radishes were common in throughout Europe and Great Britain.

The radish was one of the first vegetables introduced into the New World. Radishes were already under cultivation in Mexico in 1500 and in Haiti in 1565. The radish quickly caught on in the Americas and by 1848, there were 8 different varieties listed.

Radishes are used in very different ways around the world. In China and Japan, most of the radish crop is pickled in brine, similar to the way we pickle cucumbers. In China some large radishes are grown for the oil in the seeds. In India, the rat-tailed radish is grown for its fleshy edible seed pods which reach a length of 8-12 inches, and in Egypt, one type of radish is grown for its top greens only.

Radishes grow quickly, some maturing in 3 weeks from seed, in cool weather. Radishes should always be planted in succession plantings every 10 days to 2 weeks from the earliest possible time in the spring when the ground can be worked until early summer. For a fall crop start 6-8 weeks before the first frost date. Plant seeds for small radishes ½ inch deep in rows 6-8 inches apart. Thin seedlings to 2-3 inches apart. Plant seeds for large radishes 2 inches apart in rows 18 inches apart. Thin seedlings to 4-6 inches apart. Harvest small, round radishes when they are the size of large marbles. Do not leave radishes in the ground because they will quickly become woody and tough. Radishes can be harvested and stored in plastic bags in the refrigerator and will keep their flavor and crispness for weeks. Large radishes should be harvested before the first hard frost.

The cooler weather and shorter days of fall don’t have to mean the end of the harvest from your garden. If you plant some of these classic root crops now, you can still enjoy fresh homegrown produce well into late autumn.

If you’re a salad-loving gardener, planting a fall garden full of leafy greens is a sure way to extend the harvest season, and if you sow a bed full of short season root vegetables, you can add some variety, and a lot more crunch, to your plate. Before you go out and buy seed, check the average first frost date for your area, and plant accordingly.

Here are four classic root crops that are well suited to fall gardens:

Carrots: Carrots are fairly easy to grow from seed, but as with all seeds that require shallow planting, the surface of the soil must stay evenly moist for germination. Covering the beds with a row cover (or a low tunnel) will help hold the moisture in, or lay the row cover right on the surface of the soil and remove it when most of the seeds begin to sprout. Select seeds of carrot varieties with a shorter time to harvest, and when thinning the rows, harvest some of the baby carrots for a sweet and crunchy treat. For some variety in taste and color, plant several different types of carrots, such as purple or white ones.

Beets: If you were traumatized by having to eat canned beets as a kid, you might want to give these root vegetables another try by growing some of your own and eating them fresh from the garden, either raw (thinly sliced beets make great chips for a veggie platter) or cooked. Beet seeds are a bit deceiving, as they aren’t single seeds, but rather a cluster of several seeds, so thinning the rows of beets is a must (and as with carrots, the baby beets that get thinned out can go right into a salad). There are differently colored and sized beets, so planting a mix of varieties will yield a diversity of color and flavor in both the beet roots and the leaves (which are also edible).

Radishes: Radishes are one of the quickest vegetables to mature, depending on the specific variety, with some reaching harvest size in just 30 days. It’s possible to do several successive plantings of radishes in the fall, spaced about a week apart, for a steady supply. If you’ve steered clear of radishes because they tend to be too ‘spicy’ for you, look for some of the sweeter varieties, and sow several different types to learn which ones your family enjoys the most. Radishes can also be grown in the same row as leafy greens, as they will mature and be harvested first, which will then help to thin out the rows of lettuce or other greens.

Turnips: Turnips don’t tend to be high on the list of favorite vegetables for many people, but these root vegetables are easy to grow in the fall and tend to be somewhat sweeter than those grown in the spring and summer. Some turnip varieties can mature in as little as five weeks, and can be harvested early for roots that are tender and sweet. Even if you don’t care for turnips, they can be grown just for their greens, either by harvesting single leaves from each plant, or by cutting all the leaves at a point several inches above the root (the leaves will grow back for additional harvests). While rows of turnips need thinning to be able to produce sizable roots, it’s not necessary to thin turnips grown for their greens.

What are your favorite fall garden root crops?

Grow and Save Radish Seeds

How to Grow Radishes

Radishes are quick and easy to grow, and are a tasty addition to salads and roasted vegetable plates. Some radish varieties mature in one season, while others are over-wintered and produce seed in the second season.

Time of Planting

Plant radishes outdoors as soon as soil can be worked, in early to mid-spring and early fall.You can plant every 3-4 weeks for a continual harvest throughout the season.

Spacing Requirements

Sow seeds ½ inch deep in rows 2-3 inches apart.

Time to Germination

3-12 days

Special Considerations

When growing annual radishes for seed, increase spacing to 4-6 inches between plants in rows 24 inches apart. When growing biennial radishes for seed, increase spacing to 12-18 inches between plants in rows 24-48 inches apart.

Common Pests and Diseases

Radishes can be affected by flea beetle, cabbage fly, and slugs.

When and How to Harvest

Fast-maturing varieties can be harvested in as little as a month after planting. Harvest when leaves are 6 inches tall. Gently pull on the base of the stem to dislodge radishes from the soil.

Eating

Radishes are often included in salad plates or roasted vegetable dishes.

Storing

Radishes can be stored in the refrigerator for about a week.

How to Save Radish Seeds

Growing radishes for seed poses some challenges for seed savers. Radishes readily cross-pollinate, so you have to be sure to isolate your radish crop from other radish varieties, including wild radish.

Life Cycle

Annual or biennial, depending on the variety

Recommended Isolation Distance

Separate varieties by 800 feet to ½ mile.

Recommended Population Sizes

To ensure viable seeds, save seeds from at least 5 plants. When maintaining a variety over many generations, save seeds from 20-50 plants. If you’re saving seeds for genetic preservation of a rare variety, save seeds from 80 plants or more.

Assessing Seed Maturity

Radish fruits do not split open at maturity and can be left to dry in the field without fear of shattering. Fruits should be harvested when they turn brown and become brittle. In most areas this occurs between early and late summer.

Harvesting

Fruiting branches can be cut as they mature or all at once, when approximately two-thirds of the planting is seed mature. Although losing seeds to shattering is not a concern, seed quality can decrease if pods are left in the field for too long after maturity. After they are cut, the mature seed stalks should continue to dry on row cover or landscape fabric in a sheltered location. Threshing is easiest when pods are completely dry, usually after one to five days of drying.

Cleaning and Processing

Radish seeds do not shatter, so their seeds must be extracted by a method more forceful than threshing by hand. On a small scale, plants can be threshed by placing the harvested material on a trap or in a large container and treading upon it until the siliques break apart. Radish pods may not release their seeds easily even when broken open, and it may be necessary to crush fruits completely during the threshing process. On a larger scale, plants placed between two tarps can be driven over with a car or truck. Radish seeds are generally much heavier than the chaff and are easy to clean by screening and winnowing.

Storage and Viability

When stored under cool, dry conditions, radish seeds can be expected to remain viable for six years.

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Somehow, radishes have earned the reputation of being easy to grow. Possibly this is because the seeds germinate so quickly. Radishes often are planted in a child’s garden because they will oblige with seedlings before the child has lost interest and can be ready to eat in less than three weeks.

In truth, growing good radishes is not easy. The goal is a crisp, delicately piquant root, nice for slicing into salads or eating out of hand with a sprinkle of salt and a slice of buttered bread.

But as often as not, the radishes come out of the ground so hot they scald the tongue, or they are mushy in the middle instead of crisp, or they are tunneled through by root maggots. How can so much go wrong so fast?

Here, we’re talking about summer radishes, the fast-growing kind that usually are known as round, red-skinned and white-fleshed. There are many other shapes and colors of summer radishes, and any of them can be grown with the same degree of difficulty.

In the first place, “summer radish” is a misnomer. Radishes that are pleasantly tangy rather than fiery are grown in the spring or fall, not summer. The hotter the soil, the hotter the radish. Even the use of a garden row cover to keep leaf-munching flea beetles and root-maggot flies off the radishes may raise the soil temperature enough to increase the radish’s pungency.

Not only that, radishes tend to bolt to flower and seed as the days get long. (Conversely, they must have at least six hours of sun each day, or they will grow only tops and no bottoms.)

The corollary to the speed with which radishes mature is they become over-mature just as quickly. If they are not pulled and eaten within a few days of reaching maturity, radishes will keep growing and the cell walls will separate from each other. That makes the interior spongy, which is called pithiness.

Radishes also must have even soil moisture. If they are allowed to dry out and then are watered heavily, they will respond with such exuberant growth they split. Many a gape-jawed radish has been pulled from a garden after a spring thunderstorm.

The best way to improve the chances of a superior radish crop is to plant them in small quantities fairly often–say, every five to seven days, or as often as you think of it–except in July and August. You might lose a few of those sowings to maggots, heat, excess rain or pithiness, but the law of averages says some will grow to perfection.

Two or 3 feet of row is plenty. You could sprinkle a few seeds alongside a slower-growing crop like cabbage, knowing the radishes will be harvested before the cabbage needs the room. As the radishes grow, thin them by pulling some as soon as they are the size of dimes or even smaller, and add them to salads.

If you want big radishes, plant them deeply, about 1 1/2 inches deep. Planting radishes shallowly– 1/2 inch deep–results in small roots.

A favorite trick is to mix radish seeds with those of carrots or parsnips to mark the rows and help break the soil for these slow-germinating crops. Parsnips and carrots can take up to three weeks to sprout (old-timers say they go to the devil seven times before they come up), by which time the radishes will be ready to eat.

All varieties of summer radishes grow equally well or poorly, so you may as well be adventurous. “White Icicle” is a venerable variety, dating back to the 16th Century, and its carrot-shaped white roots are more resistant to pithiness than most. “Plum Purple” stays crisp longer than the average radish, and its skin is a wonderful purple-fuchsia color.

“French Breakfast” radishes are elongated and pink, with a white splash at the root end. They tend to be milder than most summer radishes; unfortunately, they’re also the quickest to become pithy.

“Easter Egg” radish isn’t really a variety; it’s a mixture of radish varieties with different skin colors. It’s amusing to grow, and it can provide radishes from the garden for a relatively extended period because not all of the varieties mature at the same time.

Although they don’t hold well in the garden, summer radishes will keep in the refrigerator drawer for a month or so, if you remove the tops.

If you miss a harvest and the radish roots have become spongy, you might leave the radishes in the ground until they bolt. Shortly after the yellow or white flowers fade, the radishes will produce seed pods, which look like tiny okra pods. Radish seed pods, picked when they are soft and green, are spicy, crunchy and nifty in a salad.

There is, in fact, a radish variety grown specifically for its pods. It’s called rat-tailed radish, and it produces long, curled seed pods that were commonly pickled in the 17th Century to serve with roasted meats.

You can keep sowing summer radishes into the fall. Radishes will handle frost, but can’t tolerate being frozen. They will take a little longer to mature as the days grow shorter, but they also will be milder in the cool weather and will hold a little longer in the garden without getting pithy. In short, they will be almost easy to grow.

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